Aircraft wings have stiffening elements, called stringers, attached to the inside surfaces of the upper and lower skins to give them bending resistance. The stringers run from root to tip along the span of the wing and must be bent to match the contour of the wing. The bending of the stringers allows for their attachment to the wing skins without introducing loads or stress into the assembly during riveting.
Traditionally, aircraft stringers have been formed in a hydraulic press using 3-point bending. The manual production of stringers is slow, requires a significant degree of operator expertise, requires frequent checks of part contour to determine where additional bends or “hits” are required, and has a significant scrap rate as parts are frequently damaged due to overloads.
The manual bending process takes at least two men to perform and the longest parts require two hours to form. Moreover, stringers are not formed in batches of the same part number, but are formed in ship sets so that a complete left and right hand set of parts are formed before repeating any particular part number.
In the manually applied bending process, the operator first makes marks along the length of the part at a set interval with a grease pencil. These marks are used to determine where the part will be deflected with a hydraulic ram. The operator will then place the flat part against the contour template and measure the gap between the straight part and template to indicate how much contour is needed at a particular location. The part may then be loaded into the press and moved to the first index mark, clamped to prevent movement, and then the hydraulic ram is brought down against the part to provide a permanent deflection. The part is then indexed to the next mark, clamped, and deflected by the ram. Periodically, the part will be taken out of the press and placed on an inspection table for the contour to be checked against the template. Gap measurements will be taken, additional marks will be made on the part where the gaps are outside of the forming tolerance, and the part will be put back in the press for additional hits. The process is iterative, involving many trips back and forth from the press to the inspection table.
Accordingly, there is a need in the field for a metal beam forming apparatus and method that allows for automated bending of metal beams. A fully or partially automated solution is desired that reduces costs due to loss, does not require the same level of operator expertise, lowers the risk of part damage due to overload, and cuts the two hour cycle time by at least one-half.